Pot’s not green.

The $3.5 billion U.S. cannabis market is emerging as one of the nation’s most power-hungry industries, with the 24-hour demands of thousands of indoor growing sites taxing aging electricity grids and unraveling hard-earned gains in energy conservation.

Without design standards or efficient equipment, the facilities in the 23 states where marijuana is legal are responsible for greenhouse-gas emissions almost equal to those of every car, home and business in New Hampshire. While reams of regulations cover everything from tracking individual plants to package labeling to advertising, they lack requirements to reduce energy waste.

Some operations have blown out transformers, resulting in fires. Others rely on pollution-belching diesel generators to avoid hooking into the grid. And demand could intensify in 2017 if advocates succeed in legalizing the drug for recreational use in several states, including California and Nevada. State regulators are grappling with how to address the growth, said Pennsylvania Public Utility Commissioner Pam Witmer.

“We are at the edge of this,” Witmer said. “We are looking all across the country for examples and best practices.”

The corporatization of what was once off-the-grid narco-agriculture is taxing electrical systems even as the nation prepares to comply with the Paris climate accord and the Environmental Protection Agency tries to reduce greenhouse gases from coal-fired power plants, which is considered the single largest domestic source of emissions that create global warming.

“Consumers seeking a green lifestyle are likely unaware that their cannabis use could cancel out their otherwise low- carbon footprint,” Evan Mills, a senior scientist for California’s Lawrence Berkeley National Laboratory, wrote in an e-mail.

Indoor growing operations in 2012 racked up at least $6 billion a year in energy costs, compared with $1 billion for pharmaceutical companies, Mills found in a seminal study he did independent of the research institution. Some larger facilities today suck down as much as $1 million in power a month.

ArcView, an Oakland, California, research firm, estimates the retail and wholesale marijuana market will reach $4.4 billion in 2016.

Cultivation operations from California beach cities to Denver’s warehouse district to District of Columbia closets are waiting months for new infrastructure to bring them power. Planners predict the escalating consumption could in some regions undo Americans’ attempts to save energy by buying more efficient refrigerators, washers and hair dryers.

With the industry just coming out of the shadows, utilities are without data to forecast its electrical needs.

“We don’t have aggregated energy audits from hundreds of grow operations that show us an energy footprint,” said John Morris, director of policy and regulatory affairs at CLEAResult, an Austin, Texas-based consultancy that works with growers and utilities. “We have utilities in the Northwest putting in new transformer substations to meet the load. Producers are having to go out and build infrastructure.”